An increasingly higher density connections are needed for circuit boards which have extremely high component packing density, the requirements for connectors, which cooperate with the boards, have become more severe and harder to meet. This is particularly true with edge connectors. After the circuit board has had all of the components placed on the surface thereof, the placement of the edge connector has become a critical feature in the method of circuit board fabrication.
The connector must have its electrical contacts connected to each of a number of circuit board leads or printed circuit pads. Once the connections are made, soldering occurs to assure that a reliable electrical connection is maintained. Consequently, if the initial connection between the board and the connector is faulty, the soldering will only serve to preserve this flawed connection. Therefore, a premium is placed on the initial connection between the board and the connector.
Because of the high packing density, the leads on the circuit board must be placed around the periphery thereof, and especially along one of the edges so that the component packing density may further be improved for the printed circuit board. These boards are used in an appropriate device such as a computer. The component packing density requires high connection density. Hence, connection density has fairly severe demands, such that problems have been encountered by the mere placement of the connector on an edge of a printed circuit board. For example, contacts have to be spaced at a spacing of about 0.050 inches center line to center line. These spacings have not been sufficient, and further density of these contacts has been obtained by placing two rows of contact in line, one over the other, each making a connection to a different printed circuit board lead or pad; a contact lead width of less than 0.020 inches has been used for the above 0.050 center line to center line connectors. Another method of obtaining the density requirement is to provide the leads or pads of the circuit board closer together, requiring a connector which has contacts which are able to be placed at a closer center line spacing.
A problem that arises with these high density connectors is that the contacts are fragile and therefore, easily damaged. Various attempts have been made to insure contact integrity, but great difficulties have arisen by the mere mechanical placement of the connector contacts on the printed circuit boards. These rather fragile and easily distortable contacts have tended to be easily damaged, and although various aids have been used, such as plastic insertion sheets to help avoid damage, the individual contacts have still been misplaced and/or have warped during soldering. While a number of attempts have been made to assure proper placement of the connector on the printed circuit board contacts after the placement of the connector has been achieved, the proper alignment has often been lacking, causing a number of reliability problems. These problems are magnified when one considers that when one contact is not functioning, because of misalignment, etc., the entire connector can be effectively useless. Consequently, contact integrity and reliability are severe problems in the assembly of circuit boards for which a series of solutions have been offered, none of which has been satisfactory.